This invention relates to a polyurethane elastomer exhibiting an improved abrasion resistance performance, and a process for the preparation thereof requiring the use of a liquid polybutadiene.
Polyurethane elastomer may be obtained by reaction of an isocyanate compound with an active hydrogen-containing compound such as, for example, a polyester or polyether polyol and, optionally, in the presence of a blowing agent. For processing convenience advantageously, the isocyanate compound is an isocyanate-terminated prepolymer prepared by reaction of an excess of an aromatic diisocyanate with a low molecular weight diol such as, for example, dipropylene glycol and/or tripropylene glycol. The blowing agent may be an inert physical blowing agent such as, for example, trichlorofluoromethane or, alternatively, a reactive agent such as, for example, water. The preparation of polyurethane elastomer by such procedures is described in, for example, patent publications E.P. 235,888; E.P. 175,733; U.S. Pat. No. 3,591,532; U.S. Pat. No. 3,901,959; U.S. Pat. No. 4,647,596 and U.S. Pat. No. 4,757,095.
Current manufacturing trends for polyurethane elastomers are driven by two dominant factors, namely, cost and environmental concern. Consideration of cost stimulates polyurethane elastomer producers to select polyether polyols over polyester polyols; consideration of environmental concerns stimulates polyurethane elastomer producers to select, when required, water in preference to certain physical blowing agents. Selection of polyether polyols can have a negative implication for physical properties of the resulting elastomer, including abrasion resistance. Similarly, use of water as blowing agent can also have a negative implication for physical properties of the resulting elastomer, including abrasion resistance and low temperature durability. Some of these deficiencies, notably low temperature durability, can be reduced by use of an isocyanate-terminated prepolymer prepared by reaction of an excess of an aromatic diisocyanate with a high molecular weight polyether diol or triol. However, there still remains the need to find a general means of enhancing the abrasion resistance of a polyurethane elastomer, optionally prepared in the presence of a blowing agent and particularly water.
Our investigations into the preparation of polyurethane elastomer has now revealed that selected liquid polybutadienes can significantly enhance the abrasion resistance of a polyurethane elastomer when prepared in the presence thereof. Such observation was unexpected in consideration of the open literature documenting the use of liquid polybutadienes when preparing a polyurethane elastomer. U.S. Pat. No. 4,242,468 discloses the use of a monohydroxylated polybutadiene, in amounts of at least 30 parts per 100 parts by weight of polyol, as a nonmigratory plasticizer in polyurethanes, the document is silent with respect to abrasion resistance. Plasticizers serve to soften material and it is generally appreciated that softer material has an inferior abrasion resistance. Pat. No. 5,079,270 discloses the preparation of polyurethane articles in the presence of a liquid polybutadiene having a molecular weight of from 1500 to 6000 wherein the polybutadiene serves as an internal mold release agent; the document is silent with respect to abrasion resistance.